For a Bluetooth library I want to call a startActivityForResult to enable Bluetooth. I want to do this in my own library project. The problem is that sartActivityForResult only works for Activities, my library is not an activity, of course my project using this library project is having an activity. I tried two things
1.
Had my library to extend Activity, so I am creating the object like a normal POJO. Hence when calling startActivityForResult it throws a null pointer.
2.
Tried to get my Activity to pass it into the constructor of my library object. I am not able to to get an activity object, only context but that doesn't help.
What can I do?
EDIT: Some Code
I have the following class in my library project:
public class mylib
{
public mylib()
{
// Do some bluetooth setup thing here
// figure out that bluetooth is not enabled so try to enable it now
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
onActivityResult()
{
// Report back that BT is enabled now
}
}
Then I have of course my Android application using this library project in onCreate() I do something like this
public class Myactivity() extends Activity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
// do all the normal stuff
mylib pojo = new mylib(); // This creates a POJO which needs to startActivityForResults(...), see above code
}
}
The two options I mentioned above
I don't see how I can convince mylib to call startActivityForResult doing
public class mylib extends Activity
doesn't seem to do the trick.
I could overload my constructor of mylib to pass in the activity object, I have no idea how to create the activity object.
Hope that makes it a bit clearer.
You can create a constructor of your java class which has parameter of type Activity like below,
public class MyClass
{
private Activity activity;
public MyClass ( Activity activity )
{
this.activity = activity;
}
}
Now you can use this activity variable to call startAcvitiyForResult from your Java class.
Related
I have a scenario where I have created library project in which I am loading the layout as well defining the method which I want to call from the Application project.
public class LibraryActivity {
public LibraryActivity() {
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.barchart_layout);
bindViews();
}
public void bindViews() {
bChart = (BarChart)findViewById(R.id.barchart);
}
public void setData(int count, float range) {
//definition of the method
// I have to user bChart view here
System.out.println("part 1 "+bChart); <---- this is null
}
Now I have successfully created the AAR project and I want to use this setData from the other project.
So when I run this From the other project By using below code
Intent in = new Intent(MainActivity.this,LibraryActivity.class);
startActivity(in);
LibraryActivity barChartCallBack = new LibraryActivity();
LibraryActivity.setData(15,25);
I got the null pointer on the bChart because my method setData got call first before oncreate so findviewbyid gives me null for the bChart.
You are setting the data on a completely different LibraryActivity object. First you tell the system with the intent to start one, then you start another one that does not get displayed, but you use it to call setData.
Read up on the android developer site:
https://developer.android.com/training/basics/firstapp/starting-activity.html
Basically you need to pass the data via extras in with the intent.
Im trying to figure a way how to call an activity that an adapter has started. Is there a way to get the instance of the activity from startactivity and make a method call into the activity ?
I'ved got an adapter that has a list
public class LanguageDownloadRVAdapter extends RecyclerView.Adapter<LanguageDownloadRVAdapter.DownloadViewHolder>{
And in this adapter, it starts a particular activity called MainActivity
context.startActivity(new Intent(context, MainActivity.class));
((Activity)context).finish();
Here is the MainActivity that it starts
public class MainActivity extends AppCompatActivity implements IabBroadcastListener{
How can I make a call from the adapter to a method in the MainActivity. (im just trying to perform inapp purchase which is implemented in the MainActivity). so how can i do something like this.
mainactivity.perform_inapp_purchase();
Try to use EventBus for passing data between activity and list adapter. You can do it in the same way for passing data between activity and fragment.
This work the same way as storing data in global variable (in a fancier way)
In the adapter:
Add a new Field private Context mContext;
In the adapter Constructor add one more parameter as below, and assign it into class level variable:
public LanguageDownloadRVAdapter(......,Context context){
//your code.
this.mContext=context;
}
In the Adapter where you want to call Activity's perform_inapp_purchase() method:
if(mContext instanceof MainActivity){
((MainActivity) mContext).perform_inapp_purchase();
}
More Generalized Approach:
If you need to use this same adapter for more than one activity then :
Create an Interface
public interface InAppPerchaceInterface{
void perform_inapp_purchase();
}
Implement this interface in activities
Then in Adapter, call like below:
if(mContext instanceof InAppPerchaceInterface){
((InAppPerchaceInterface) mContext).perform_inapp_purchase();
}
You can store the instance in the application class, but you should be careful about the memory leaks.
In the onCreate of your activity
protected void onCreate(Bundle savedInstanceState)
{
// get the instance using this and store it in the application class or in the place that you want to call from it
}
From where will you call your method?
I didn't understand the situation.
I have tried almost all the solutions from SO but no success :(.
I have a simple myJavaClass.java with a couple of functions.
One of the functions in myJavaClass : startActivity() starts MyCustomActivity
public startActivity(Context context)
{
Intent intent = new Intent(context, MyCustomActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK |Intent.FLAG_ACTIVITY_SINGLE_TOP);
context.startActivity(intent);
}
This launches MyCustomActivity() as expected.
Now I have another function in myJavaClass.java to close/finish MyCustomActivity but it is not able to do so!
I have tried
Making MyCustomActivity SingleTop in manifest and creating the activity via an intent as above
Passing an activity instance to "this" in onCreate() of MyCustomActivity and calling MyCustomActivity.activity.finish() from myJava.class but that doesnt work as well
Please help me. I have been stuck here for hours now. I know the solution is very simple and conceptual but I am a newbie. Just building Java/Android concepts!
EDIT
MyCustomActivity
public Activity activity;
OnCreate()
{
...
this = activity;
}
MyJavaClass
public closeActivity(Context context)
{
Activity customActivity = MyCustomActivity.activity;
customActivity.finish();
}
I think that what you are trying to do is fundamentally bad. For a start, outside of the Activity code, there are no guarantees that the activity still exists - the memory manager may have cleaned it up, the user may have pressed Back etc. Think of Activities as independent entities - you can start them, and you can optionally get a result back when they finish what they're doing, but that's it.
Think about whether you really have to programmatically close the activity from outside it - I'd say this is an unusual design, but there are circumstances where it may be appropriate.
If so, what I think you want is a publish/subscribe system whereby MyCustomActivity can register a listener with MyJavaClass, and then receive a callback whereupon it can 'finish' itself.
public Activity activity implements FinishListener
{
public void onCreate(...)
{
//where does MyJavaClass come from? see in a minute
MyJavaClass myjava = getMyJavaclass();
myJava.addFinishListener( this );
}
public void onFinishCallback()
{
this.finish();
}
}
and
public class MyJavaClass
{
private List<FinishListener> finishListeners = ...;
public void addFinishListener( FinishListener fl )
{
this.finishListeners.add(fl);
}
public closeActivity(Context context)
{
for ( FinishListener fl : finishListeners )
{
fl.onFinishCallback();
}
}
}
and
public interface FinishListener
{
void onFinishCallback();
}
Now the only remaining issue is how to get MyJavaClass from the Activity. That's up to you - you may already know how, you may be able to put it in your Application implementation, it could be a singleton (bad), the listeners could be static (bad) or various other options.
Oh, and don't forget to remove the listener again in the Activity's onDestroy() method!
Just try this....
public closeActivity(Activity _activity)
{
_activity.finish();
}
you can't finish activity from other class until you have the reference of instance of Activity in that class, give the reference in that class and call finish() method to stop the activity.
activity.finish();
First to explain how projects are setup:
Android Library project with two classes:
UserActivity - uses static field in HolderClass
HolderClass - this one has static field Data
Android Application that references Library project, has only one class:
StarterActivity - when app is started, in onCreate it sets static field Data to some value, and it starts UserActivity
Now, the problem is: sometimes I get java.lang.NullPointerException for that static field Data - as if I never initialized it (or value got deleted in meantime). It never happened on my test device, but I keep getting error reports from client devices. I can only guess how that happens - maybe user navigates away from app, then comes back and system recreates whole application context, but in that context HolderClass has empty static field Data?
My question:
Is initialization of that static field from Activity's onCreate wrong approach? Should I put data in ApplicationContext? Or do something else?
I am open for all suggestions.
P.S. If you have problem visualizing from description, here is how everything I've said would look in code:
// IN ANDROID APP PROJECT
public class StarterActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// just start activity in library
Intent myIntent = new Intent(this, AutolaunchActivity.class);
startActivityForResult(myIntent, 1);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// exit when activity from library exits
finish();
}
}
// IN LIBRARY PROJECT
public class HolderClass {
public static String Data;
}
public class UserActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// init layout
}
public void someButtonClicked() {
HolderClass.Data.trim();
}
}
The usual ways of sharing data between activities is documented here. The intermittent nature of the error suggests a timing problem to me. Are you using threads in some of your initialization? Also, do you know if the NPE happening in StarterActivity or UserActivity?
OK, this was basically the problem of global variables - in the end I've solved it by reading this answer: How to declare global variables in Android?
I have a beginners problem. Here is my situation:
I want to start a new activity from the main activity. The code to launch the new activity is found in a separate class file. I seem to be passing the wrong arguments and I am ending up in a nullpointerexception when trying to launch the new activity. The new activity launches fine when I place the code in the main activity class file, therefore the second activity and the manifest are fine. Here is a sample of my code:
In my main activity class where I instanciate the second class (THIS IS MY MAIN ACTIVITY. I OMITTED THE REST BECAUSE I DO NOT THINK IT IS RELATED TO THE PROBLEM):
Tester mytest = new Tester();
mytest.test(this);
In my second class file (THIS IS NOT AN ACTIVITY; IT IS A CLASS THAT IS INSTANTIATED IN THE ACTIVITY):
public class Tester extends Activity {
Intent myIntent;
public void test (Context context) {
myIntent = new Intent (Intent.ACTION_VIEW);
myIntent.setClass(context, newActivity.class);
thebutton.setOnClickListener(
new OnClickListener() {
public void onClick(View v) {
startActivity(myIntent);
}
}
):}
When I perform the click I receive a nullpointerexception at startactivity. Can anyone enlighten me on this please?I am sure that I am wrongly using the context.
Activities are started with Intents. Please read the Android Application Fundamentals first and try the Hello World app :)
I understood that you will use your separate Tester class at all cost ;) so I'm trying to adapt and help you out there.
First of all, don't let your class inherit from Activity. This won't help you, cause this calls will probably not have any valid context. Activity somehow implements the template pattern, providing you key method like onCreate(...), onPause(...) etc and is instantiated by the Android OS.
If you still want to use the class, you have to pass in the context. Probably you're aiming for some MVC/MVP pattern structure, anyway.
public class Tester {
private Context context;
public Tester(Context context){
this.context = context;
}
public void test () {
final Intent myIntent = new Intent(context, NewActivity.class);
//guess this comes from somewhere, hope through a findViewById method
thebutton.setOnClickListener(
new OnClickListener() {
public void onClick(View v) {
context.startActivity(myIntent);
}
}
)};
}
}
This would be a proposed solution from my side. A problem I still see here is on how you retrieve the button in that test() method. In order to have that work properly you have to retrieve it from some View class (with view.findViewByid(R.id.myButton)) or to create it dynamically and associate it with the view during the onCreate(...) of your Activity (probably using an Inflater).